GPS not accurate on 3GS

I just got an iPhone 3GS. I noticed that wherever I go in the city (downtown Vancouver) my iPhone GPS on Google maps shows a huge bubble of where I might be, and the blue dot in the center is usually very off.

However, if I turn on Wifi (and do not connect to any networks... in fact, I've never once associated with any wifi network since owning the device) the GPS location in google maps becomes just the exact blue dot, and is very accurate.

How does having wifi on help it locate me? For example, I turn on the iPhone's wifi in my condo, and GPS gives an exact fix of where I am... but the iPhone isn't connected to any wifi networks, and the phone can only see 3 SSID's of some random wifi routers of neighbors in my building??

What gives? I don't want to leave wifi on all the time just so I can use GPS... it is an unnecessary drain on my battery since I don't use wifi ever.

I just got an iPhone 3GS. I noticed that wherever I go in the city (downtown Vancouver) my iPhone GPS on Google maps shows a huge bubble of where I might be, and the blue dot in the center is usually very off.

However, if I turn on Wifi (and do not connect to any networks... in fact, I've never once associated with any wifi network since owning the device) the GPS location in google maps becomes just the exact blue dot, and is very accurate.

How does having wifi on help it locate me? For example, I turn on the iPhone's wifi in my condo, and GPS gives an exact fix of where I am... but the iPhone isn't connected to any wifi networks, and the phone can only see 3 SSID's of some random wifi routers of neighbors in my building??

What gives? I don't want to leave wifi on all the time just so I can use GPS... it is an unnecessary drain on my battery since I don't use wifi ever.

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In the downtown, the buildings are probably blocking your GPS signal from at least some satellites. The wi-fi on allows apple's servers to figure out what hot spots are nearby, and locate you based on a directory of hot-spot locations.

It shouldnt be doing that.
Maybe its a bug fixable with a restore.
If you can never get an accurate GPS lock with wifi off then try to restore or take it to Apple for an exchange.
Mine shows me within 5-10 feet at google maps even at exactly what corner of my house Im sitting in.

It's A-GPS, or assisted GPS. If it has a poor GPS signal, it'll use WiFi and/or cell location data as an assist, until (or if) it gets a good enough signal. WiFi mapping can be very accurate, since they have a database by lat/lon of the access point.

I've noticed that on the 3GS, even inside, I get the pin on the map, whereas on the 3G I would only get the bulls-eye-radius indoors. In my limited and completely unscientific testing, I think that it's simply dropping a pin in the center of the radius that it would normally show. For example, right now I'm in my house and it's showing the pin at the nearest corner (1 house and a few yards away), whereas if I was outside (with line-of-sight to the GPS satellites) it would be a bit more accurate (showing the pin closer to my driveway). I think cmaier is right in that Wi-Fi is simply helping it get a better idea of where you are, and the blue pin is simply an approximation and not the exact coordinates of where you're standing.

But how would it have lat/long of the wifi "hotspots" nearby if they are just my random neighbors' wifi routers that the phone is seeing (I looked in the SSID list)?

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I've always figured A-GPS worked even with the Wi-Fi option turned off (figured that it only turned off the use of it for data).

Anyway, Skyhook is the company that Apple uses for their assisted GPS. (this was way back even before the 2.0 SDK came out) Basically, they went around the nation (probably in a car like Google Street View) and mapped out the location of all the Wi-Fi hotspots they came across and stored their longitude and latitude. Of course in neighborhoods especially, hotspots change quite frequently, whether people took them down or new ones came up, so it's not totally accurate (the database that is). But in terms of location it should be.

I've always figured A-GPS worked even with the Wi-Fi option turned off (figured that it only turned off the use of it for data).

Anyway, Skyhook is the company that Apple uses for their assisted GPS. (this was way back even before the 2.0 SDK came out) Basically, they went around the nation (probably in a car like Google Street View) and mapped out the location of all the Wi-Fi hotspots they came across and stored their longitude and latitude. Of course in neighborhoods especially, hotspots change quite frequently, whether people took them down or new ones came up, so it's not totally accurate (the database that is). But in terms of location it should be.

That's how they know the longitude and latitude.

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Can anyone With a 3gs let let me know if Their gps accuracy changes with wifi on versus wifi off (when not connected to any network in both cases) when there are no wifi networks in the area?

The GPS in my new 3GS is terrible. On EDGE, it's about 3 miles off. On 3G it's about 1 mile off, and with Wifi it's about 50 feet off. I'm going away this week and I'll check it out again to see if it's just my area that sucks. Otherwise I'll take it to the Apple store and compare it with the units they have there and see if it gives me similar results (if the store units are more precise then I'll exchange mine).

The GPS in my new 3GS is terrible. On EDGE, it's about 3 miles off. On 3G it's about 1 mile off, and with Wifi it's about 50 feet off. I'm going away this week and I'll check it out again to see if it's just my area that sucks. Otherwise I'll take it to the Apple store and compare it with the units they have there and see if it gives me similar results (if the store units are more precise then I'll exchange mine).

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GPS should have nothing to do with any of the 3G/Edge/wi-fi networks. If you've got a clear view of the sky and whichever of the 32 satellites that make up the constellation happen to be overhead at that moment, you should be good. By clear view i mean in multiple directions, you might do OK up next to one building, but in a "canyon" between 2 buildings, or a real canyon between 2 mountains, chances are there are not enough satellites visible to triangulate your position from.
As far as your area sucking, GPS is available worldwide.

Hmm I looked into this further, and you're right about the Skyhooks thing... how odd that the phone can find out the coordinates of wifi networks around me, without even connecting to them.

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It's not odd. The wifi networks don't know where they are so connecting to them (if you could) would not help.

All you are doing is connecting to skyhook (probably over the 3g) and submitting names (probably mac address) of the networks around you. Skyhook look up in its database and tells you where it thinks you are.

It works well for me. Indoors GPS does not work at all. With WIFI off I get a circle on the map about half a mile across. I am presuming this is from the cell tower triangulation only. Turning on the wifi improves the location to about 50 feet.

So I originally posted this thread because my GPS was not working well without Wifi on... it turns out my GPS really wasn't working at all, and that I was only getting cell tower triangulation when GPS was off. Resetting the network settings on my 3GS solved the problem, and now GPS actually works to show my exact location (without wifi on). I can tell it must be GPS now, because the blue dot s exact and has a pulsating effect now which it never had before (before there was just a big blue semi-transparent circle around the dot).

I've always figured A-GPS worked even with the Wi-Fi option turned off (figured that it only turned off the use of it for data).

Anyway, Skyhook is the company that Apple uses for their assisted GPS. (this was way back even before the 2.0 SDK came out) Basically, they went around the nation (probably in a car like Google Street View) and mapped out the location of all the Wi-Fi hotspots they came across and stored their longitude and latitude. Of course in neighborhoods especially, hotspots change quite frequently, whether people took them down or new ones came up, so it's not totally accurate (the database that is). But in terms of location it should be.

That's how they know the longitude and latitude.

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Also the more people with iPhones or using skyyhook database devices on other phones like the G1 helps add or delete routers in the area.
Say if I got a new router at my house. My iPhone would use my Gps on my iPhone to gather my location then it would look for routers in my area if it found the same router in my area multiple times it would automatically add it to skyhools database and assign it a location to the maps app. This helps skyhook so the don't "have to" send cars out and search wifi networks every year or so.

This goes the same way for routers removed from the area. If I searched for my location and got rid of my router it would notice that that device is gone and automatically remove it from their database.

When the GPS is turned on, it takes time to determine your location. If the iPhone has a rough estimate of where you are (e.g, from wifi hotspots), determining your location is faster (much faster in some cases).

I don't know about the iPhone, but handheld GPS units can take minutes to lock onto your location, if they don't have a good starting guess (and that assumes good GPS signals -- ones not blocked or obscured by buildings, etc.).

So I originally posted this thread because my GPS was not working well without Wifi on... it turns out my GPS really wasn't working at all, and that I was only getting cell tower triangulation when GPS was off. Resetting the network settings on my 3GS solved the problem, and now GPS actually works to show my exact location (without wifi on). I can tell it must be GPS now, because the blue dot s exact and has a pulsating effect now which it never had before (before there was just a big blue semi-transparent circle around the dot).

I spoke too soon. This only seem to solve the problem for me temporarily... it stopped working again later today and I had to reset my network settings again outside I hope I don't have to keep doing this.

I spoke too soon. This only seem to solve the problem for me temporarily... it stopped working again later today and I had to reset my network settings again outside I hope I don't have to keep doing this.

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Are you sure there's something wrong? The GPS can sometimes take a minute or more to lock on, especially if the sky is partially obstructed, if it's been a while since the last time it was used, or if you've moved any significant distance from where it was last used (if the iPhone can't get a good starting location estimate via wifi or 3G/EDGE triangulation).

Note that going outside gets you better GPS signals, and your reset might not really be necessary (the going outside part is the key ).

If your GPS really is that bad, and you can show the guys at Apple, they'll give you another phone. I went yesterday for my yellow screen but they ended up giving me a new phone because my GPS is always off. If it's that bad, show somebody at apple and theyll swap it out for a new phone.

just need to be in direct contact with a satellite. think of it as the same when you don't get reception for a phone call/text

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but with 2.2.1 it would always work even inside! ever since the 3.0 it has been so off and uses triangular location. it's a wide known problem and seems to be because of 3.0. Apple needs to hurry up and release an update.

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